Calibration of the photometric G passband for Gaia Data Release 1

TL;DR

This paper calibrates the Gaia DR1 G passband by comparing observed and synthetic photometry, correcting the passband curve, and establishing a precise Vega zero point for accurate stellar measurements.

Contribution

It provides a corrected G passband curve and zero point calibration for Gaia DR1, improving photometric accuracy over previous nominal values.

Findings

The nominal G passband was too blue for DR1 photometry.

A power-law correction with exponent 0.783 removes the color term.

The Vega zero point for the corrected passband is 0.070±0.004 mag.

Abstract

Context. On September 2016 the first data from Gaia were released (DR1). The first release included photometry for over 10^9 sources in the very broad G system. Aims. To test the correspondence between G magnitudes in DR1 and the synthetic equivalents derived using spectral energy distributions from observed and model spectrophotometry. To correct the G passband curve and to measure the zero point in the Vega system. Methods. I have computed the synthetic G and Tycho-2 BV photometry for a sample of stars using the Next Generation Spectral Library (NGSL) and the Hubble Space Telescope (HST) CALSPEC spectroscopic standards. Results. I have found that the nominal G passband curve is too blue for the DR1 photometry, as shown by the presence of a color term in the comparison between observed and synthetic magnitudes. A correction to the passband applying a power law in lambda with an exponent of 0.783 eliminates the color term. The corrected passband has a Vega zero point of 0.070$\pm$0.004 magnitudes.